Chlorinated biphenyls are highly regulated compounds that have been accumulating in the environment over the years. There are many sites that have been contaminated with polychlorinated biphenyls (PCBs). Therefore, it is a high priority to have simple, rapid, and accurate methods for characterizing such sites and quantitively monitoring the remedial clean-up of such sites.
A current methodology for determining the presence or amount of polychlorinated biphenyls (PCBs) in a sample involves extracting the sample with an organic solvent and then using a gas chromatograph (GC) equipped with an electron capture detector (ECD) to analyze the extract. The problems encountered with this method are inherent to the analytical technique. For instance, the procedure is time-consuming and expensive since the GC/ECD runs only one sample at a time, requires about 40-60 minutes per test sample, and highly trained technical personnel are required to perform the testing and maintain the equipment. Even portable gas chromatograph methods are not rapid enough to dramatically lower the cost of analysis.
Another approach for detecting PCB pollutants in the environment is the utilization of immunoassay technology. Immunoassay offers a method which has similar sensitivity as gas chromatography, while being more rapid, simpler, and less expensive.
One such immunoassay that has been developed for detecting PCBs is radioimmunoassay. Radio immunoassays use reagents incorporating radioisotopes as tracers. The relative distribution of radiolabelled tracer and unlabelled PCBs from the sample allows determination of PCB concentrations in the sample. Iodine tracers are often used in the method to detect the PCBs.
Another immunoassay method is taught by U.S. Pat. No. 5,145,790 to Mattingly et al., for detecting the presence or amount of PCBs in a test sample using fluorescence polarization. The assay is performed by adding a known concentration of a tracer labeled with a detectable fluorescent moiety and a known concentration of a PCB-specific antibody to a test sample to form a mixture, incubating the mixture to form labeled tracer-antibody and PCB-antibody complexes. Free tracer and the tracer-antibody complexes are excited with polarized light and the polarization of the emitted light is measured to determine the presence or amount of tracer-antibody complexes formed, leading to a measure of the presence or amount of PCB in the test sample. Mattingly's method requires the use of a polarized light source and laboratory instrumentation.
While these immunoassay methods provide advantages over GC/ECD methods for screening of PCBs, they are subject to difficulties. When manually performed, these assay methods usually require an operator to carefully manage a number of reagents and operations. The outcome of a test is dependent upon successfully completing each operation. As a result, there are many opportunities for systematic errors.
Other difficulties with the above-mentioned immunoassay methods are that they require expensive equipment for automation, may involve the handling of radioactive materials, are not easily manipulated in field applications, and have a limited range of PCB detection.
Chemiluminescence is another method that is being used in immunoassays. Chemiluminescence is light emission that arises during the course of a chemical reaction. Light is produced when molecules, formed in an electronically excited state, decay to the ground state.
Chemiluminescent reactions provide a very sensitive detection system because no external light source is required as would be the case for fluorescence or colorimetric immunoassay methods. All the light reaching a detector originates from the chemical reaction with no contribution from scattered excitation radiation or background fluorescence from a substrate which limits the useful sensitivity of fluorescent detection. The instrumental background signal is essentially zero and hence the contribution of a single chemiluminescent reaction can be detected as a single photon.
The principle advantages of employing such reactions to monitor PCB immunoassay are that they are extremely sensitive and rapid. The labels are also relatively stable, have high specific activity and can take part in amplification reactions. This feature allows simple and rapid detection of trace levels of chlorinated biphenyls. Further, chemiluminescence analysis does not require complex instrumentation, but can be performed simply with a light intensity meter or films.
There is a need for a practical, effective chemiluminescence immunoassay method that detects PCBs in environmental samples quickly and accurately at field sites.
There is also a need to provide a sensitive test that detects low chlorine-content chlorinated biphenyls because of dechlorination processes in certain environmental conditions.